Peak power reduction methods in distributed charge pump systems

ABSTRACT

A distributed charge pump system uses a delay element and frequency dividers to generate out of phase pump clock signals that drive different charge pumps, to offset peak current clock edges for each charge pump and thereby reduce overall peak power. Clock signal division and phase offset may be extended to multiple levels for further smoothing of the pump clock signal transitions. A dual frequency divider may be used which receives the clock signal and its complement, and generates two divided signals that are 90° out of phase. In an illustrative embodiment the clock generator comprises a variable-frequency clock source, and a voltage regulator senses an output voltage of the charge pumps, generates a reference voltage based on a currently selected frequency of the variable-frequency clock source, and temporarily disables the charge pumps (by turning off local pump clocks) when the output voltage is greater than the reference voltage.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention generally relates to voltage supplies forintegrated circuits, and more particularly to distributed charge pumpsystems used to power electronic memory structures such as dynamicrandom-access memory (DRAM).

2. Description of the Related Art

Power management has become a dominant concern in the development ofdata processing systems. Excess power usage is not only costly andinefficient, but also leads to heat management problems. These problemsare particularly pronounced in computer systems having large amounts ofmemory. State of the art computer systems typically use dynamicrandom-access memory (DRAM) which is preferable over other memorystructures such as static random-access memory (SRAM) because DRAM ismore dense. However, DRAM can be more power intensive in circuit blocksfor active power supply generation and refresh. SRAM uses a flip-flopmemory cell but DRAM uses a capacitor-based memory cell which, due tocurrent leakage, must be regularly refreshed. DRAM can consume asignificant portion of a system's overall power.

Power management has become even more challenging with the advent of newmemory technologies like embedded DRAM (eDRAM). This new design relieson the silicon-on-insulator (SOI) technology pioneered by InternationalBusiness Machines Corp. using deep-trench capacitors. Deep-trench(3-dimensional) capacitors have a reduced footprint on the semiconductorsubstrate, and an eDRAM array has about one-third the area of acomparable DRAM array. Reducing the size of the memory makes it easierto embed the array on the same integrated circuit chip, e.g., amicroprocessor or an application-specific integrated circuit (ASIC), toprovide a system-on-a-chip solution. An exemplary commercialmicroprocessor might devote up to 60% of its surface area to memory.Replacing conventional DRAM with eDRAM cells allows the chip designer tobuild smaller chips and reduce the length of wire that data must travelas it commutes around the chip, resulting in the fastest memory accesstimes ever recorded. Embedding memory further permits much wider busesand higher operation speeds and, due to the much higher density ofeDRAM, larger amounts of memory can potentially be used.

An eDRAM array requires an on-chip power supply having precise high andlow voltages (positive and negative) for the word lines that drive therows of the memory array. The high voltage is used to activate a wordline, and the low voltage is for standby. FIG. 1 depicts a conventionalpower supply for an eDRAM array. Power supply 10 includes a referencegenerator 12, two regulators 14 a, 14 b, two pump cores 16 a, 16 b, anda clock source 18. Clock source 18 (phase-locked loop) provides a singleclock signal to each of the pump cores 16 a, 16 b, for example in therange of 20-300 MHz. Pump core 16 a provides a high voltage level V_(pp)to an active voltage rail 20, while pump core 16 b provides a lowvoltage level V_(wl) to a standby voltage rail 22. The high voltagelevel V_(pp) may be referred to a positive voltage and the low voltagelevel V_(wl) may be referred to as a negative voltage, but these termsare relative and those skilled in the art will appreciate that both thehigh and low voltage levels may be positive voltage values. V_(pp) maybe in the range of 1.4 to 1.8 volts and V_(wl) may be in the range of−0.3 to −0.7 volts.

Rails 20, 22 have pairs of taps connected to respective word linedrivers 24-1, 24-n. Each word line driver 24 is used to activate acorresponding row of memory cells in eDRAM array 26. In this exampleeDRAM array 26 is 1200 cells wide, i.e., each word line is connected to1200 cells in that row. A memory address for a requested memory block isdecoded by memory control logic (not shown) and the resulting signal isused to activate the appropriate word line driver which then switchesthe voltage for that word line to V_(pp) while the other word lines aremaintained at V_(wl). The switching circuitry within a word line driver24 uses a separate supply voltage V_(dd) (e.g., around 1.0 volt). Senselines 28 a, 28 b connected to the inputs of word line drivers 24 areused to provide feedback to regulators 14 a, 14 b. Regulators 14 a, 14 bdetermine an upper limit of the pump voltages and temporarily disable apump core if the output voltage exceeds the limit. Reference generator12 generates an internal stable voltage that is used by regulators 14 a,14 b for comparison purposes. Reference generator may be a band gapcircuit or voltage divider, or an external reference can be provided.

Various pump designs can be used to deliver the voltages from pump cores16 a, 16 b, including for example the Cockcroft-Walton voltagemultiplier, the Dickson charge pump, and the Nakagome voltage doubler.The Cockcroft-Walton voltage multiplier uses a ladder network ofcapacitors and diodes or switches connected to a low voltage input. As acharge cascades through the capacitors it successively increases tofinally yield a higher voltage at the output. The Dickson charge pumpoperates in a similar manner but in the Dickson design the nodes of thediode chain are coupled to the inputs via capacitors in parallel insteadof in series. The Nakagome voltage doubler uses switched capacitorswhose output nodes are connected to cross-coupled transistors.

Peak electrical current in these charge pumps occurs at the clock signaledges, i.e., rising and falling. While peak current is not particularlytroublesome for a single charge pump, it can become excessive in largersystems having multiple charge pumps. For example, a microprocessor chipmay include an on-board level 3 (L3) cache memory having 32 megabytes ofmemory employing 96 charge pumps. If these pumps all run on the sameclock signal, charge pump peak power and transient current supplycurrent is multiplied by a factor of 96, which would significantlyburden the system power budget and heat sink cost.

Methods have been devised which address peak power consumption involtage supplies for integrated circuits, but these methods still havevarious disadvantages. In the construction of application-specificintegrated circuits (ASICs), a granular DRAM cell is provided with itsown pump and oscillator in a single circuit block. This approach doesnot work well in high performance systems with large embedded DRAM sinceinstantaneous switching power can still be many times higher. Half-cycleclock edge usage does not affect peak current in switched-capacitor(cross-coupled) charge pumps since both clock phases are already used.In a more recent clock distribution system design (Montecito), aphase-locked loop (PLL) circuit feeds many digital frequency dividers(DFDs) several of which are phase and frequency aligned. Each DFDcontains a delay locked loop (DLL) and a state machine that dynamicallyselect among 64 DLL phases. At the second level clock buffer (SLCB)level, regional active deskew phase comparators are used to reduce skewsdue to process, voltage and temperate variations. Half-rate 0° and 90°differential clocks are multiplied to return to the full rate clock atthe SLCB level. This multiplicity of blocks is inefficient for largeon-board designs, and also presents problems with variability and thepower burden on the clock network itself. In another clock distributionsystem used for polysilicon thin-film transistor displays, delayelements are employed to achieve phase offsets. This approach requires atime constant match between pump operation and the delay circuit blocks.The delay block is part of the clock excitation path and contributes topump system power usage. Phase offset by delay stages does not work wellfor newer technologies (with FO4 delays in the neighborhood of 10picoseconds) since it may take up to 250 such delay stages to move justone clock edge of a 100 MHz clock by 25% of its period.

On-die regulated voltage level generation is becoming essential toreduce system cost and power delivery complexity in large chips withmultiple power islands. In particular, supply generation for eDRAM wordlines in server class applications entails special challenges because ofthe stringent power, performance, cell retention, variability, anddistribution requirements. It would, therefore, be desirable to devisean improved charge pump system which can overcome the foregoing problemsbut still have an efficient energy conversion topology. It would befurther advantageous if the system could easily be optimized for activeand leakage power.

SUMMARY OF THE INVENTION

It is therefore one object of the present invention to provide animproved clock system for a voltage supply having multiple charge pumps.

It is another object of the present invention to provide such a systemwhich does not entail an excessive number of delay stages but stillreduces peak power usage in a distributed charge pump system,particularly one utilizing switched-capacitor charge pumps.

It is yet another object of the present invention to provide such asystem which can be further optimized for voltage regulation.

The foregoing objects are achieved in a distributed charge pump systemgenerally comprising first and second charge pumps, a clock generatorwhich provides a first clock signal, a delay element connected to theclock generator which creates a second clock signal that is out of phasewith the first clock signal, a first clock divider which receives thefirst clock signal and generates a first lower-frequency signal thatclocks the first charge pump, and a second clock divider which receivesthe second clock signal and generates a second lower-frequency signalout of phase with the first lower-frequency signal that clocks thesecond charge pump, to offset peak current clock edges for each chargepump and thereby reduce overall peak power. Preferably, the clockdividers divide the clock frequency by two, the second clock signal isapproximately 180° out of phase with the first clock signal, and thesecond lower-frequency signal is approximately 90° out of phase with thefirst lower-frequency signal. The clock signal division and phase offsetmay be extended to multiple levels for further smoothing of the pumpclock signal transitions. The clock dividers may be integrated into adual frequency divider comprising a first input which receives a firstclock signal, a second input which receives a second clock signal thatis out of phase with the first clock signal (e.g., 180°), a firstdivider circuit connected to said first and second inputs whichgenerates a first divided signal having a frequency less than that ofthe first clock signal (e.g., half), and a second divider circuitconnected to said first and second inputs which generates a seconddivided signal having a frequency equal to that of the first dividedsignal and out of phase with the first divided signal (e.g., 90°). Thedual frequency divider outputs may be selectively disabled.

The charge pumps may be switched-capacitor charge pumps. In anillustrative embodiment the clock generator comprises avariable-frequency clock source including a 2 GHz source signal and acontrollable frequency divider that selectively divides the sourcesignal by 4, 8 or 16, to generate intermediate clock frequencies at 500MHz, 250 MHz, or 125 MHz. The clock generator may further include afrequency-tunable oscillator, and a multiplexer which selects betweenthe clock source and the oscillator to output the first clock signal.The charge pump system may further include a voltage regulator whichsenses an output voltage of the charge pumps, generates a referencevoltage based on a currently selected frequency of thevariable-frequency clock source, and temporarily disables the chargepumps (by turning off local pump clocks) when the output voltage isgreater than the reference voltage.

The above as well as additional objectives, features, and advantages ofthe present invention will become apparent in the following detailedwritten description.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention may be better understood, and its numerousobjects, features, and advantages made apparent to those skilled in theart by referencing the accompanying drawings.

FIG. 1 is a block diagram of a conventional power supply circuit fordriving word lines of an embedded dynamic random-access memory (eDRAM)array;

FIG. 2 is a high-level schematic diagram of a clock circuit for adistributed charge pump system constructed in accordance with oneembodiment of the present invention;

FIG. 3 is a timing diagram for the three clock signals shown in FIG. 2;

FIG. 4 is a detailed schematic diagram of one embodiment of aswitched-capacitor charge pump that may be used in the distributedcharge pump system of the present invention;

FIGS. 5A and 5B are high-level schematic diagrams of alternativeconstructions for a frequency divider that may be used in thedistributed charge pump system of the present invention;

FIG. 6 is a detailed schematic diagram for the AND/NOR gate combinationlogic shown in FIG. 5B;

FIG. 7 is a high level schematic diagram of a preferred embodiment for adual frequency divider that may be used in the distributed charge pumpsystem of the present invention; and

FIG. 8 is a high-level schematic diagram of a clock circuit for adistributed charge pump system constructed in accordance with a moresophisticated embodiment of the present invention.

The use of the same reference symbols in different drawings indicatessimilar or identical items.

DESCRIPTION OF THE PREFERRED EMBODIMENT(S)

With reference now to the figures, and in particular with reference toFIG. 2, there is depicted a simplified embodiment 30 of a distributedcharge pump system constructed in accordance with the present invention.Distributed charge pump system 30 is generally comprised of a clocksource 32, a delay element 33 which receives the clock signal “clk” fromclock source 32, a first frequency divider 34 a which receives a delayedclock signal from delay element 33, a second frequency divider 34 bwhich receives the undelayed clock signal from clock source 32, twobuffers 36 a, 36 b respectively connected to the outputs of frequencydividers 34 a, 34 b, and two charge pumps 38 a, 38 b driven byrespective clock signals “clk_1” and “clk_2” from buffers 36 a, 36 b.Clock source 32 may for example be a phase-lock loop circuit utilizingan oscillator. Delay element 33 is an inverter in this embodiment butmay comprise other circuit structures which exhibit a known delay inconveying the clock signal. Dividers 34 a, 34 b in this embodimentdivide the frequency by a divisor of two but other divisors could beused; exemplary details for the dividers are discussed below inconjunction with FIGS. 5A, 5B and 6. Buffers 36 a, 36 b are used onlyfor timing adjustment and are not necessary for the most basicimplementation of the invention. Distributed charge pump system 30 ispart of an integrated circuit (IC) chip, and charge pumps 38 a and 38 bare used to supply regulated voltages to other circuit components on thesame IC chip such as an embedded dynamic random-access memory (eDRAM)array. The charge pump clock network is separate from the functionalclock for the eDRAM array.

FIG. 3 is a timing diagram for the three clock signals illustrated inFIG. 2. The front-end clock delay produces approximately 90° phaseseparation in the “clk” signal to offset peak current clock edges foreach pump cluster, which minimizes aggregate peak AC currents at anygiven moment. In this implementation the “clk_1” signal transitions(rises or falls) approximately halfway in time between the transitionsof the “clk_2” signal, and vice-versa, but the invention contemplatesother phase differences as well.

Charge pumps 38 a, 38 b are preferably designed with an internalslew-optimized voltage doubling topology, cross-coupled to transfercharges efficiently during both clock phases. One example of a positivepump engine 38′ which may be used with the present invention isillustrated in further detail in FIG. 4. Positive pump engine 38′includes two switched capacitors 42, 44. Capacitors 42, 44 arepreferably deep-trench capacitors. Their capacitance may vary dependingupon the desired pump capacity, i.e., the ability to maintain thedesired voltage across the output rail for a sustained load. In theillustrative embodiment the capacitance is around 50-1000 picofarad.

The input node of capacitor 42 is coupled to a power supply voltageV_(dd) by a p-type metal oxide semiconducting (PMOS) transistor 46 andto electrical ground by an n-type metal oxide semiconducting (NMOS)transistor 48. PMOS transistor 46 is controlled by a first gating signalderived from a first clock signal “clk_i_wide” and NMOS transistor 48 iscontrolled by a second gating signal derived from a second clock signal“clk_i_narrow”. The duty cycle of the “clk_i_wide” signal is greaterthan 50% while the duty cycle of the “clk_i_narrow” is less than 50%.The two signals are non-overlapping for break-before-make switching toavoid leakage. Each of these clock signals pass through a series ofbuffers (inverters) which provide a desired time delay.

The input node of capacitor 44 is similarly coupled to the power supplyvoltage V_(dd) by another PMOS transistor 50 and to electrical ground byanother NMOS transistor 52. PMOS transistor 50 is controlled by a thirdgating signal derived from the “clk_i_narrow” signal and NMOS transistor52 is controlled by a fourth gating signal derived from the “clk_i_wide”signal. The clock signals again pass through one or more buffers orinverters which provide a desired time delay such that the input node ofcapacitor 42 is charging (connected to V_(dd)) when the input node ofcapacitor 44 is discharging (connected to ground) during the first clockphase, and the input node of capacitor 44 is charging when the inputnode of capacitor 42 is discharging during the second clock phase.

The pumping devices 46, 48, 50, 52 are preferably of non-body contacttype to conserve area. The region 54 containing the inverters andpumping devices (the charging circuit) is preferably thin-oxide in orderto support lower voltages. This two-phase inverter topology combinedwith the use of wide and narrow clock signals provides superior clockedge control while reducing clock loading, and is relatively compact.

Two cross-coupled PMOS transistors 56, 58 are respectively connected tothe output nodes of capacitors 42, 44. The source terminals oftransistors 56, 58 are interconnected to provide the output voltageV_(pp) of the charge pump. Each output node is also coupled to areference voltage by respective PMOS transistors 60, 62; for thepositive pump embodiment this reference voltage is the power supplyvoltage V_(dd). The gate of PMOS transistor 60 is coupled to the pumpoutput voltage V_(pp) by a PMOS transistor 64 and to electrical groundby an NMOS transistor 66. The gates of PMOS transistor 64 and NMOStransistor 66 are in turn controlled by the output of a level shifter68. The high voltage rail of level shifter 68 is connected to the pumpoutput voltage V_(pp). Level shifter 68 has a positive polarity and itsinput is the “clk_i_narrow” signal. The gate of PMOS transistor 62 issimilarly coupled to the pump output voltage V_(pp) by another PMOStransistor 70 and to electrical ground by another NMOS transistor 72.The gates of PMOS transistor 70 and NMOS transistor 72 are in turncontrolled by the output of another level shifter 74. The high voltagerail of level shifter 74 is connected to the pump output voltage V_(pp).Level shifter 74 has a negative polarity (its output is the logicalcomplement of the input) and its input is the “clk_i_wide” signal. Thistopology for the side charging devices 60, 62 provides a particularlywell-regulated voltage level output. The output nodes of each capacitor42, 44 are also connected to clamp circuits 76 which are used in anoverride mode to disable the charge pumps.

A local pump clock circuit 40 is used to generate the “clk_i_wide” and“clk_i_narrow” signals. Two adjustable signals “starve_p” and “starve_n”control the edge separation for the “clk_i_wide” and “clk_i_narrow”signals. A pump enable signal (“pump_en”) is used for the override(clamp) mode; during normal operation of the charge pump the pump enablesignal is turned on. When disabled (“pump_en” turned off), wide outputis set to 1 and narrow output is set to 0 to shut off both phases of thecharge pump.

A negative pump engine analog to positive pump engine 38′ may beconstructed to provide a low level regulated voltage (V_(wl)) byswitching the polarities and inputs of the level shifters and switchingthe reference voltages for the side transistors. Further detailsregarding the construction and operation of the positive and negativepump engines, pump clock 40, level shifters 68, 74, clamps 76,alternative designs for charge pumps, and other features may be found inU.S. patent application Ser. No. 11/927,784 which is herebyincorporated. Those skilled in the art will appreciate however that thepresent invention is not limited to any specific charge pumpconstruction. For example, inverted pump clock inputs can be fed to twosingle-ended pumps that share the same clock source.

Two alternative designs for the frequency dividers are depicted in FIGS.5A and 5B. In both of these designs, frequency division is essentiallyaccomplished by feeding the inverted output of a slave stage latch backto the input of a master stage latch. The clock signal “clk” forfrequency divider 34-1 shown in FIG. 5A is connected to the control lineof a transmission gate 80 (nfet/pfet), i.e., transmission gate 80 isconducting when “clk” is active. Its output is connected to a storagecell 82 (flip-flop) and to an inverter 84. The output of inverter 84 isfed back through another inverter 86 to the input of a secondtransmission gate 88 which is controlled by the complement of the clocksignal “clk_b”. The output of transmission gate 88 is connected toanother storage cell 90 and to a third inverter 92. The output ofinverter 92 is connected to the input of transmission gate 80. Theoutput of inverter 84 is the output of divider 34-1, the “div2” signalwhich has half the frequency of the “clk” signal.

In the frequency divider 34-2 shown in FIG. 5B, the clock signal “clk”is an input to two AND gates 94, 96, and the invert clock signal “clk_b”is an input to another two AND gates 98, 100. The output of each ANDgate 94, 96, 98, 100 is connected to one input of a respective NOR gate102, 104, 106, 108. The outputs of NOR gates 102, 104 are cross-coupledto their other inputs, as are the outputs of NOR gates 106 and 108. Theoutput of NOR gate 102 is also connected to an input of AND gate 98, andthe output of NOR gate 104 is also connected to an input of AND gate100. The output of NOR gate 106 is also connected to an input of ANDgate 96, and the output of NOR gate 108 is also connected to an input ofAND gate 94. The output of NOR gate 104 is the true output of divider34-2, the “div2” signal which has half the frequency of the “clk”signal; the output of NOR gate 102 is the complement output “div2_b”.

The AND/NOR gate combination logic 110 of FIG. 5B is preferablyimplemented as further illustrated in FIG. 6. The two inputs to the ANDgate are designated as a1 and a2, while the second (cross-coupled) inputto the NOR gate is designated as b. Input a1 is connected to the gate ofa pfet i-type field-effect transistor) 112 and to the gate of an nfet(n-type field-effect transistor) 114. Input a2 is connected to the gateof a pfet 116 and to the gate of an nfet 118. Input b is connected tothe gate of a pfet 120 and to the gate of an nfet 122. The drain of pfet120 is connected to the network power supply (V_(dd)) and its source isconnected to the drains of pfets 112 and 116. The source of pfet 112 isconnected to the drain of nfet 122 and to a node 124 which also connectsto the source of pfet 116 and to the drain of nfet 114. The source ofnfet 114 is connected to the drain of nfet 118. The sources of nfets 118and 122 are connected to electrical ground. The signal at node 124 isthe output of the circuit, i.e., the output of the NOR gate in theAND/NOR gate combination logic 110. This construction is more compactthan separate AND and NOR gates, but is not to be construed in alimiting sense as other circuit designs may be used in the dividers, andthose skilled in the art will again appreciate that the presentinvention is not limited to any specific frequency divider construction.

While distributed charge pump system 30 utilizes two separate frequencydividers 34 a, 34 b as shown in FIG. 2, the invention may insteadadvantageously utilize a dual frequency divider as illustrated in FIG.7. Dual frequency divider 34-3 employs two frequency divider circuits34-1 a and 34-1 b that share a single pair of clock inputs. In frequencydivider circuit 34-1 a the forward transmission gate is controlled bysignal “clk(2f, Ψ+180°)” and the feedback transmission gate iscontrolled by signal “clk(2f, Ψ)”. In frequency divider circuit 34-1 bthe forward transmission gate is controlled by signal “clk(2f, Ψ)” andthe feedback transmission gate is controlled by signal “clk(2f,Ψ+180°)”. The output of frequency divider circuit 34-1 a is signal“clk(f, Φ)”, and the output of frequency divider circuit 34-1 b issignal “clk(f, Φ+90°)” (f represents clock frequency, and Ψ and Φrepresent clock phases). Thus, dual frequency divider 34-3 receives aclock signal and its complement as inputs, and generates two outputswhich are 90° out of phase and have half the frequency of the originalclock signal. This construction has the further advantage of preventingloop oscillations when the input clock is disabled since the forwardtransmission gate in one divider circuit will be off while the feedbacktransmission gate in the other divider circuit will simultaneously beoff. The outputs may optionally be buffered, or may be connected torespective buffered AND gates 126 a, 126 b which are used to disabledual frequency divider 34-3 using an “enable” signal input, in order tosuppress phase effects and latch set-up time differences.

A more sophisticated embodiment of a clock network for a distributedcharge pump system using the present invention is shown in FIG. 8. Clocknetwork 130 includes a controllable divider 132, a small,frequency-tunable oscillator 134, a multiplexer 136 which receivesinputs from controllable divider 132 and frequency-tunable oscillator134, a plurality of first-level frequency dividers 138 which receive theoutput of multiplexer 136, a plurality of delay elements (buffers) 140connected to respective first level frequency dividers 138, and aplurality of second-level frequency dividers 142 a, 142 b whereinsecond-level frequency dividers 142 a receive an input from a respectivebuffer 140 and second-level frequency dividers 142 b receive an inputfrom a respective first-level frequency divider 138. Each second-levelfrequency divider 142 a, 142 b clocks a separate charge pump.

In this implementation first-level frequency dividers 138 aresingle-ended, and second-level frequency dividers have two phase-shiftedoutputs, e.g., using dual frequency dividers 34-3. Buffers 140 add 90°of phase to the clock input for second-level frequency dividers 142 a,with the result that transitions for the four clock signals “clkA”,“clkB”, “clkC”, “clkD” of a single pump cluster are interleaved, i.e.,offset at eight different phases (the four clock signals are all out ofphase). This smoothing of peak power usage yields significant powerreduction in systems having large numbers of charge pumps, e.g., anon-chip cache memory for a microprocessor. The frequency dividers alsoconveniently act as local (or sector) clock buffers. Those skilled inthe art will appreciate that this multi-level use of dividers can befurther expanded to more than two levels, and in more complexembodiments the dividers can have divisors greater than two.

Charge pump efficiency is related to clock frequency, and the presentinvention may easily be adapted to take advantage of this dependency byproviding controllable divider 132 as a variable-frequency clock source.Experimentation suggests that the most efficient frequency range for areference voltage (V_(dd)) of 0.8 to 1.0 volts is roughly 100-500 MHz,so in this embodiment controllable divider 132 receives a 2 GHz clocksignal and selectively divides that signal by a divisor of 4, 8 or 16,to generate intermediate clock frequencies at 500 MHz, 250 MHz, or 125MHz. The divisor may be selected at the factory or in response to arun-time determination. The flexibility of the clock generator frequencyallows for pump efficiency optimization in the event of variations inhardware characteristics.

The further inclusion of frequency-tunable oscillator 134 facilitatesburn-in, very low-frequency array functional testing, and other similarsituations. Under those conditions, the pump clock is supplied from theon-chip oscillator via selection by multiplexer 136 to maintain pumpefficiency and desired voltage level. When implemented in localizedfashions, oscillators can be designed with preset start-up states toprovide known phase offsets between different localities.

Pumped voltage levels may be further regulated in various manners, suchas by comparing the divided sense point voltage to a reference level,and turning each pump on and off by enabling or disabling its clockaccordingly. A voltage regulator 144 is used for this purpose. Voltageregulator 144 receives the clock signal from multiplexer 136 andcompares a reference level to the sensed voltage (V_(pp)) using acomparator. Although any sensitive comparator will suffice, thecomparator is preferably one of the reduced-jitter digital comparatorsdescribed in U.S. patent application Ser. No. 11/464,672 which is herebyincorporated. The reference voltage may vary considerably depending uponthe pump design, in the range of 0 volts (ground) to the power supplyvoltage (V_(dd)). The sense voltage is sampled according to theintermediate frequency output of controllable divider 132, i.e., at afrequency that is higher than the local pump clock frequency but lowerthan the clock frequency for the powered electronic structure, e.g., theeDRAM array. If the sensed voltage is greater than the indicatedreference level, the “pump_control” signal is activated to temporarilyturn off the charge pumps (by disabling the clock signals from pumpclock 40).

To prevent a high-power condition due to delays in comparator decisionregistration, a latch structure which regulates switching thresholds maybe incorporated prior to the pump clock enable feed. To control ripples,each pump output may also employ deep-trench capacitors, in addition todistributed deep-trench capacitors and circuit loads on the distributiongrids. Multiple feedback sense points can be taken from calculatedlocations in a word line grid (V_(pp) and V_(wl)) to control the pumpduty cycle and minimize RC drops. A 15 KΩ shunt to V_(dd) or ground maybe added to individual positive and negative pump outputs, respectively,to block low-frequency noise and ringing.

The present invention thus significantly reduces peak power consumptionin distributed charge pump system, with low overhead and low cost. Theresulting power profile is highly controllable and predictable. Inparticular the invention is very useful for an on-chip, word line dualsupply generation system for 45 nm SOI eDRAM technology. This adaptiveon-chip voltage solution greatly enhances eDRAM operation andscalability.

Although the invention has been described with reference to specificembodiments, this description is not meant to be construed in a limitingsense. Various modifications of the disclosed embodiments, as well asalternative embodiments of the invention, will become apparent topersons skilled in the art upon reference to the description of theinvention. It is therefore contemplated that such modifications can bemade without departing from the spirit or scope of the present inventionas defined in the appended claims.

1. A distributed charge pump system in an integrated circuit comprising: at least first and second charge pumps; a clock generator which provides a first clock signal, said clock generator including a variable-frequency clock source responsive to a division select signal, a frequency-tunable oscillator responsive to an enable signal and to a frequency control signal, and a multiplexer which selects between said variable-frequency clock source and said frequency-tunable oscillator to output the first clock signal; a delay element connected to said clock generator which creates a second clock signal that is out of phase with the first clock signal; a first clock divider which divides the first clock signal by two to generates a first lower-frequency signal that clocks said first charge pump, said first clock divider including a first input which receives the first clock signal, a second input which receives a complement of the first clock signal, a first transmission gate controlled by said first input, a first storage cell connected to an output of said first transmission gate, a first inverter having an input connected to said output of said first transmission gate, a second inverter having an input connected to an output of said first inverter, a second transmission gate having an input connected to an output of said second inverter, and controlled by said second input, a second storage cell connected to an output of said second transmission gate, a third inverter having an input connected to said output of said second transmission gate, and an output connected to an input of said first transmission gate, and a divider output connected to said output of said first inverter; and a second clock divider which divides the second clock signal by two to generate a second lower-frequency signal, out of phase with the first lower-frequency signal, that clocks said second charge pump.
 2. The distributed charge pump system of claim 1 wherein said charge pumps are switched-capacitor charge pumps.
 3. The distributed charge pump system of claim 1 wherein: the second clock signal is approximately 180° out of phase with the first clock signal; and the second lower-frequency signal is approximately 90° out of phase with the first lower-frequency signal.
 4. A clock network for a distributed charge pump system of an integrated circuit , comprising: a clock generator which provides a first clock signal; a plurality of first frequency dividers connected to said clock generator which create divided clock signals having a frequency less than that of the first clock signal; delay elements connected respectively to outputs of said first frequency dividers; and a plurality of second frequency dividers, some of said second frequency dividers connected respectively to said outputs of said first frequency dividers to generate first and second pump clock signals, and others of said second frequency dividers connected respectively to said delay elements to generate third and fourth pump clock signals, wherein the first pump clock signal drives a first charge pump, the second pump clock signal drives a second charge pump, the third pump clock signal drives a third charge pump, the fourth pump clock signal drives a fourth charge pump, and the first, second, third and fourth pump clock signals are all out of phase, wherein at least one of said second frequency dividers includes a first input which receives the divided clock signal, a second input which receives a complement of the divided clock signal, a first divider circuit connected to said first and second inputs which generates the first pump clock signal, and a second divider circuit connected to said first and second inputs which generates the second pump clock signal.
 5. The clock network of claim 4 wherein said clock generator includes: a clock source; a frequency-tunable oscillator; and a multiplexer which selects between said clock source and said frequency-tunable oscillator to output the first clock signal.
 6. The clock network of claim 4 wherein said first and second frequency dividers divide clock frequency by two.
 7. The clock network of claim 4 wherein said clock generator includes: a clock source; and a controllable frequency divider connected to said clock source.
 8. The clock network of claim 7 wherein said clock source provides a 2 GHz source signal and said controllable frequency divider selectively divides the source signal by 4, 8 or 16, to generate intermediate clock frequencies at 500 MHz, 250 MHz, or 125 MHz.
 9. A distributed charge pump system in an integrated circuit comprising: at least first and second charge pumps; a clock generator which provides a first clock signal; a delay element connected to said clock generator which creates a second clock signal that is out of phase with the first clock signal; a first clock divider which receives the first clock signal and generates a first lower-frequency signal that clocks said first charge pump, said first clock divider including a first input which receives the first clock signal, a second input which receives a complement of the first clock signal, a first transmission gate controlled by said first input, a first storage cell connected to an output of said first transmission gate, a first inverter having an input connected to said output of said first transmission gate, a second inverter having an input connected to an output of said first inverter, a second transmission gate having an input connected to an output of said second inverter, and controlled by said second input, a second storage cell connected to an output of said second transmission gate, a third inverter having an input connected to said output of said second transmission gate and an output connected to an input of said first transmission gate, and a divider output connected to said output of said first inverter; and a second clock divider which receives the second clock signal and generates a second lower-frequency signal, out of phase with the first lower-frequency signal, that clocks said second charge pump. 